Method of plating on stainless steel

ABSTRACT

A process by which a metal may be plated on a stainless steel metal substrate whereby the final electroplated composite possesses greatly improved adherence. Said process involves the electrodeposition of a nickel strike layer on the stainless steel base metal prior to plating a &#39;&#39;&#39;&#39;Woods strike&#39;&#39;&#39;&#39; nickel electroplating bath in which the nickel therein is in the form of nickel bromide and the acid in the bath is hydrobromic acid. The composition and operating conditions of said bath comprise: NiBr2 100-800 g./l. HBr 0.2%-20% by weight Current Density 5-200 a.s.f. Bath Temperature 60*-115* F.

Unified iaees Fame 1151 3,6ese61 Garvey Feb, 29, 1972 [54] METHOD OF PLATHNG ON STAINLESS Primary Examiner-G p sTEEL Attorney-John P. Hazzard [72] inventor: Bruce .H. Garvey, Cleveland, Ohio [57] ABSTRACT [73] Assignee: Kewame Company Bryn Mawr A process by which a metal may be plated on a stainles steel [22] Filed: Sept 3,1970 metal substrate whereby the final electroplated composite possesses greatly improved adherence. Said process involves [2]] Appl- N04 70,559 the eiectrodeposition of a nickel strike layer on the stainless steel base metal prior to plating a Woods strike nickel elec- [52 us. (:1 ..204/49, 204/40, 204 41, troplating bath in which the nickel therein is in the form of 29/1965 nickel bromide and the acid in the bath is hydrobromic acid. [51] Int. Cl. ..C23b 5/08,C23b 5/50 The composition and operating conditions of said bath com- [58] Field of ee1rch ..204/41, 40, 49; 29/ 1 96.6 pris na 100-800 g./l. [56] References Cited HBr 1 0.2%-20% by weight UNITED STATES PATENTS 2,800,440 7/1957 Brown ..204/49 5-200 3,003,933 10/1961 Atkinson ....204/49 0 0 3,186,925 6/1965 Kushner ..204/41 M Willi-Lil;

l ms iei r w METHOD OF PLATHNG ON STAKNLESS STEEL The instant invention relates to a process and metal composite formed thereby, whereby various metals may be adherently applied to a stainless steel substrate.

The invention further relates to the electrodeposition of a nickel strike from a bromide type Woods strike directly on the stainless steel substrate prior to deposition of said metal which is desired to be firmly adhered to the stainless steel substrate.

The use of stainless steels as substrates under other electrodeposited metals is not new to the art but such has achieved only limited application in various industries due to the fact that it is particularly difficult to secure adequate adhesion to the stainless steel substrate. Stainless steels themselves vary greatly in the degree of adherence that can be obtained through electrodeposited coatings. The instant invention as indicated previously, greatly improves the adherence of numerous metals wished to be deposited on stainless steels in general. However, the present invention has its greatest applicability when used in conjunction with the stainless steels on which it is more difficult to deposit an adherent coating.

The present invention will be described in more detail with respect to a particular stainless steel, namely, type 446 stainless steel although it is equally applicable to other varieties of stainless steel.

In the manufacture of Geiger Mueller radiation detector tubes, it is desirable to provide on the internal surface of the stainless steel body of said radiation detector tube a metal deposit which is inert to the corrosive gases contained therein. It has been attempted in the past to electroplate platinum or other metal on the internal walls of such stainless steel tubes. Such attempts to electroplate platinum directly onto the inner surface of such stainless steel tubes were unsuccessful in view of poor adhesion on the platinum. Numerous pretreatments were tried on the stainless steel surface prior to deposition of the platinum with little success. Utilizing some complex pretreatments of the stainless steel, however, would result in some success, but the rejection rate of such tubes due to nonadherence of platinum or other noble metal clearly pointed out the commercial unfeasibility of such a process.

Adequate adherence by the adjacent metal layers is of course, dependent on the intermetallic bond established by said materials. The strength of the intermetallic bond required will, of course, depend on the end use of the article and the conditions it must endure. The instant invention thus, is most beneficial when applied to articles which are subject to high temperature changes or those which must later undergo considerable forming or bending.

Likewise, the surface condition of this stainless steel substrate is also extremely important. Whether the substrate has been rolled, heat-treated, annealed, etched or been subject to various cleaning cycles or other pretreatment, the practice of the present invention produces a more adherent metal layer due to the intermediate nickel strike when compared to directly applying said metal layer to said stainless steel substrate.

The theory behind the instant invention is to apply an intermediate metallic layer which itself is highly adherent to a stainless steel substrate and said intermediate metallic layer is such that it also produces a high adherent bond with the metal plating thereover.

The metal layer which is desired to be adherently attached to the stainless steel substrate through the intermediate nickel strike layer of the instant invention can be any of numerous metals, for example, brass, bronze, cadmium, chromium, copper, gold, indium, iridium, nickel, palladium, platinum, rhodium, silver, tin or zinc. Likewise, more than one metallic electroplate may be utilized over said intermediate nickel strike layer which effects the intermetallic bond with the stainless steel which results in the improved adherence contemplated by the instant invention.

As stated earlier, such intermediate metallic layer in the practice of the present invention is a nickel strike from a bromide Woods strike bath. Woods strike baths are well known to those skilled in the art of electroplated nickel. Such baths generally are made up of nickel chloride and hydrochloric acid. The use of such standard Woods strike baths, however, will not result in the improved adherence contemplated by the instant invention whether on the more easily plated stainless steels or in the case of the more difficulty plated stainless steels wherein such standard Woods strike baths produce only a deposit possessing inadequate adherence.

As is well known to those skilled in the art, it is possible to electroplate nickel onto some stainless steels and secure moderately good adherence by the use of standard Woods strike nickel electroplate bath. Such typical bath contains 32 oz. per gallon NiCl -6l-l- O (240 g./l.) and 16 fluid oz. per gallon HC] (72% percent by weight). Such a nickel strike is deposited at room temperature under standard current density. Onto such a strike layer can be deposited one or more metals which possess some adherence. However, in all cases improved adherence is obtained when the bromide Woods strike of the instant invention is utilized. in general, we have found that stainless steels become more difficult to use as a substrate on which a strongly adherent metal electrodeposit is desired as the chromium content of the stainless steel increases. With certain high chromium content stainless steels and particularly with type 446 stainless steel, adherence of the nickel strike from a standard Woods strike was inadequate and could not be appreciably improved by varying the concentration of nickel chloride and/or HCl over wide ranges. During our experimentation in which tests were made in an attempt to improve the adherence of the standard chloride Woods strike to the stainless steel, it was found that even after various types of pretreatments including several etchings, adequate adherence could not be obtained by using a standard Woods strike type bath in which the nickel chloride was between l50-300 g./l. or more and the hydrochloric acid concentration filled from about 02-20 percent in the bath.

Such standard Woods strike baths must be modified by replacing the nickel chloride and hydrochloric acid therein with nickel bromide and hydrobromic acid. The composition of such a bromide Woods strike bath may vary widely. The nickel bromide concentration can vary from approximately -800 g./l. while the l-lBr content can vary from 0.2-20 percent by weight. The current density utilized in such a bath is generally in the range of 5-200 amps per sq. ft. and the plating time can be anything up to approximately 10 minutes although it is preferred to use as short as possible plating times. Preferably such baths are operated at room temperature, however, such may be operated up to a temperature of approximately F.

The preferred bath concentration for this bromide type Woods strike electroplate bath of the instant invention is to utilize a nickel bromide concentration of approximately 500 g./l. and a hydrobromic acid concentration of approximately 0.4 percent by weight. Operation of said preferred bath would be at room temperature with a current density of approximately 16 amps per sq. ft. for approximately 5 minutes.

To more fully describe the instant invention, a typical example is given hereinafter wherein said bromide-type Woods strike is utilized to form a strongly adherent nickel deposit on the interior surface of a type 446 stainless steel tube which is to be used in Geiger Mueller radiation detection device after it is further plated with platinum and assembling is completed. Such a typical Geiger Mueller radiation detection device is fully described in US. Pat. No. 3,342,538 issued Sept. 19, 1967.

EXAMPLE A stainless steel type 446 length of tubing having a wall thickness of 0.010 in. was first cathodically cleaned in a conventional alkaline cleaner at -210 F. for 15 seconds. After a cold water rinse the stainless steel tube was dipped for a few seconds with agitation in a 20 percent by volume and 7% milliliters per liter of 48 percent by weight solution of HBr. After removing and rinsing the nickel-plated stainless steel tube, it was electroplated with platinum from a conventional platinum plating bath. The platinum bath was made up as follows:

Ammonium nitrate 13 02.

Sodium nitrate 1.5 02.

Platinum compound g. (as Platinum) Ammonium hydroxide 200 ml.

Water 1 gal. Temperature 210 F.

Current density 60 ats.l.

Adherence of all layers to the substrate was excellent. In each of the plating cycles, the stainless steel tube acted as the cathode and the anode consisted of a centrally aligned wire running through the stainless steel tube.

I claim:

1. A method of firmly adhering a metal deposition to a stainless steel substrate comprising electrodepositing a nickel strike on said stainless steel substrate prior to application of said metal deposition, said nickel strike being electroplated from an aqueous nickel electroplating bath comprising to 800 grams per liter nickel bromide and 0.2 to 20 percent by weight hydrobromic acid, said electrodeposition of said nickel strike being effected at a current density between 5 and 200 amps per square foot.

2. A method of firmly adhering a metal deposition to a stainless steel substrate comprising electrodepositing a nickel strike on said stainless steel substrate prior to application of said metal deposition, said nickel strike being electroplated from an aqueous-nickel electroplating bath comprising approximately 500 grams per liter nickel bromide and approximately 0.4 percent by weight hydrobromic acid, said electrodeposition of said nickel strike being effected at a current density between 5 and 200 amps per square foot.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. qfiL 861 Dated Eebmlamz 2 1912 Inventor(s) Bruce J. Garvey It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Abstract, line 5, after the word "plating" insert of said metal. The nickel strike is electroplated from Column 2, line 16, change "72 to read --l2 Signed and sealed this 11th day of July 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-1050 (10-69) USCOMM-DC 60376-P69 b 0.5, GOVERNMENT PRINTING OFFICE: 1969 0-366-334 

2. A method of firmly adhering a metal deposition to a stainless steel substrate comprising electrodepositing a nickel strike on said stainless steel substrate prior to application of said metal deposition, said nickel strike being electroplated from an aqueous nickel electroplating bath comprising approximately 500 grams per liter nickel bromide and approximately 0.4 percent by weight hydrobromic acid, said electrodeposition of said nickel strike being effected at a current density between 5 and 200 amps per square foot. 